Journal Article

Cannabis Use and Psychosis: A Longitudinal Population-based Study

J. van Os, M. Bak, M. Hanssen, R. V. Bijl, R. de Graaf and H. Verdoux

in American Journal of Epidemiology

Published on behalf of Johns Hopkins Bloomberg School of Public Health

Volume 156, issue 4, pages 319-327
Published in print August 2002 | ISSN: 0002-9262
Published online August 2002 | e-ISSN: 1476-6256 | DOI: https://dx.doi.org/10.1093/aje/kwf043
Cannabis Use and Psychosis: A Longitudinal Population-based Study

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Cannabis use may increase the risk of psychotic disorders and result in a poor prognosis for those with an established vulnerability to psychosis. A 3-year follow-up (1997–1999) is reported of a general population of 4,045 psychosis-free persons and of 59 subjects in the Netherlands with a baseline diagnosis of psychotic disorder. Substance use was assessed at baseline, 1-year follow-up, and 3-year follow-up. Baseline cannabis use predicted the presence at follow-up of any level of psychotic symptoms (adjusted odds ratio (OR) = 2.76, 95% confidence interval (CI): 1.18, 6.47), as well as a severe level of psychotic symptoms (OR = 24.17, 95% CI: 5.44, 107.46), and clinician assessment of the need for care for psychotic symptoms (OR = 12.01, 95% CI: 2.24, 64.34). The effect of baseline cannabis use was stronger than the effect at 1-year and 3-year follow-up, and more than 50% of the psychosis diagnoses could be attributed to cannabis use. On the additive scale, the effect of cannabis use was much stronger in those with a baseline diagnosis of psychotic disorder (risk difference, 54.7%) than in those without (risk difference, 2.2%; p for interaction = 0.001). Results confirm previous suggestions that cannabis use increases the risk of both the incidence of psychosis in psychosis-free persons and a poor prognosis for those with an established vulnerability to psychotic disorder. Am J Epidemiol 2002;156:319–27.

Keywords: cannabis; drug utilization; psychoses, substance-induced; psychotic disorders; schizophrenia; Abbreviations: BPRS, Brief Psychiatric Rating Scale; CI, confidence interval; CIDI, Composite International Diagnostic Interview; DSM-III-R, Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised; OR, odds ratio; T1, time 1 (between baseline and 1997); T2, time 2 (between 1997 (T1) and 1999).

Journal Article.  7024 words. 

Subjects: Public Health and Epidemiology

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